Isoflurane-induced hypotension does not cause impairment in pulmonary gas exchange.

Induced hypotension during anaesthesia can result in deterioration in gas exchange with increases in intrapulmonary shunting and physiological deadspace. Cardiovascular stability has been previously demonstrated with isoflurane-induced hypotension but the effects on gas exchange have not been carefully studied. We have examined the shunt fraction (QS/QT) and physiological dead space to tidal volume ratio (VD/VT) before, during and following deliberate hypotension in twelve patients. Group I (n = 6) received an isoflurane-oxygen-air mixture with an FIO2 of 0.5 while Group II (n = 6) received an isoflurane-oxygen mixture with an FIO2 of 1.0. Mean blood pressure was reduced from 76 +/- 2 mmHg to 47 +/- 2 mmHg in the combined group. Neither QS/QT nor VD/VT changed significantly during the hypotensive state in either group. We conclude that isoflurane induced hypotension is associated with minimal pulmonary derangement.